Previously, the NLRB had threatened to sue all four states. However, those plans were delayed for a period of time as compromise talks began before later breaking down when the NRLB wanted the talks to be conducted in secret. Now, the NLRB in an effort to save money, has announced it would be suing two states–Arizona and South Dakota–to invalidate their constitutional amendments.

Unions like using card check because it makes it easier to win unionization campaigns. Organizers can gather signature cards quietly until they get a majority of workers, making it more difficult for an employer to mount an opposition campaign. Congressional Republicans blocked passage of the card-check bill.

In January, the labor board threatened to sue four states, including South Carolina and Utah, which also have constitutional amendments barring card check. But in a letter sent on Friday to the four states’ attorneys generals, N.L.R.B. officials said they were suing just two states to conserve legal resources.

The labor board’s acting general counsel, Lafe Solomon, said the government reserved “the right to initiate a suit against the other two states at the appropriate time.”

N.L.R.B. officials evidently hope that victories in the Arizona and South Dakota cases would serve as precedents to invalidate the South Carolina and Utah prohibitions.

All four states’ Attorneys General would vigorously defend their states, according to the Associated Press.

“South Dakota’s constitutional amendment is consistent with existing federal law,” South Dakota Attorney General Marty Jackley said Monday. “The NLRB’s continued threatened federal litigation against the states is unwarranted.”

NRLB officials thought they might be able to work out a compromise earlier this year when attorneys general for the four states issued a letter saying the amendments were not trying to supersede federal law. But Jackley said compromise talks broke down over the NLRB’s request for a confidentiality agreement. He said such an agreement would “limit our ability to explain to our citizens any course of action in this important matter.”

Whether or not the NLRB ultimately prevails in its suit against the states, what will be interesting is whether or not the whole issue of card check and its inherent flaws as a union organizing tactic will be subject to deserved scrutiny in open court.